1. Field of the Invention
This invention relates to the field of suspensions for hard disk drives. More particularly, this invention relates to the field of electrical interconnects from disk drive suspension flexures to PZT microactuator motors.
2. Description of Related Art
Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) is mounted proximate a distal end of load beam 107. The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end nearest to base plate 12 which is swaged or otherwise mounted to an actuator arm. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end.
Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface.
Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only voice coil motor 112 moves suspension 105.
In a DSA suspension, as for example in U.S. Pat. No. 7,459,835 issued to Mei et al. as well as many others, in addition to voice coil motor 112 which moves the entire suspension, at least one microactuator is located on the suspension in order to effect fine movements of the magnetic head slider to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. In the discussion that follows, for simplicity the microactuator maybe be referred to simply as a “PZT,” although it will be understood that the microactuator need not be of the PZT type.
FIG. 2 is a top plan view of the prior art suspension 105 in FIG. 1. Two PZT microactuators 14 are affixed to suspension 105 on microactuator mounting shelves 18 that are formed within base plate 12, such that the PZTs span respective gaps in base plate 12. Microactuators 14 are affixed to mounting shelves 18 by non-conductive epoxy 16 at each end of the microactuators. The positive and negative electrical connections can be made from the PZTs to the suspension's flexible wiring trace and/or to the grounded base plate by a variety of techniques.
The suspension includes both a load beam which is formed of stainless steel, and a flexure that includes the electrical circuit. The electrical circuit typically comprises a stainless steel support layer, an insulator such as polyimide thereon, copper signal traces thereon, and an insulating and protective cover layer such as polyimide thereon.
FIG. 3 is a top perspective closeup view of suspension of FIG. 2 in the area of one of the PZT microactuators 14. Electrical interconnect contact pad 22 on the underside of PZT 14 as viewed in FIG. 3, which defines the electrical interconnection to one surface electrode of PZT 14, is shown in hidden lines.
FIG. 4A-4F are a process flow diagrams illustrating the process for forming a suspension flexure or circuit or electrical interconnect contact pad 22 or a flying lead, and attaching it to a PZT motor 170, according to the prior art. The process begins with a sheet of stainless steel 110 on which a layer of insulating material 120 such as polyimide is coated. A layer of conductive material 130 such as copper or copper alloy is then deposited on the polyimide 120. Typically, before copper layer 130 is deposited, a thin layer of chromium is deposited on the polyimide by sputtering, followed by a thin layer of copper deposited by sputtering, which ensures that the electrodeposited layer of copper 130 will adhere to the polyimide. The stainless steel 110 and polyimide 120 are then patterned and etched away from the copper pad 132 to form the flying lead or contact pad 22.
FIG. 4F is a side sectional view of shows could be either an electrical interconnect flying lead or a contact pad 22 as shown in FIG. 3 with the contact pad 22 having a central copper contact 132 with stainless steel 110 and polyimide 120 formed in a generally circular pattern around the central copper contact 132. A flying lead is defined by an exposed contact of the conductive layer in a circuit for making electrical contact to a component, with the circuit continuing both to the left and right thereof and being at least capable of having electrical components attached to the lead on one or both sides of the exposed pad 132 of conductive material. In other configurations, the exposed copper pad 132 constitutes a terminus, there being stainless steel 110 and polyimide 120 on only one horizontal side thereof. The unsupported copper pad 132, whether it be a flying lead or circular contact pad 22 as shown in FIG. 4 or a terminus as shown in FIG. 3, is then typically plated with a protective plating such as nickel 138 on the exposed surfaces of copper, followed by a finish plating such as gold 150, 152. The combined nickel and gold layers will be referred to simply as the Ni/Au plating or layer. During suspension assembly a conductive epoxy 140 is applied between the copper pad 132 and the PZT motor 170 which includes PZT material 172 and metallized first and second sides 174, 175. Conductive epoxy 140 is then thermally cured to make a mechanical/electrical connection between the flexure and the PZT motor 170. Typically, the conductive epoxy 140 from the PZT surface to the copper pad surface is approximately 20-40 μm thick.